Device for adjusting the sensitivity level of an implantable medical device

Abstract

An implantable cardiac stimulation device has an atrial detector that detects atrial events of a patient's heart, and a memory in which sequences of IEGM signals are stored, having a predetermined length, and an analyzing unit that analyzes the sequences to determine if the stored sequences contain atrial events having a lower amplitude than the current sensitivity setting of the atrial detector. A control unit is connected to the atrial detector to adjust the sensitivity setting thereof to a threshold that is determined based on the aforementioned analysis of the IEGM signals.

1. An implantable cardiac stimulation device comprising:
 an atrial detector having an amplifier configured to detect incoming atrial IEGM signals that may include a P-wave, said atrial detector having adjustable sensitivity settings to detect said incoming IEGM atrial signals; 
 a control unit connected to said atrial detector supplied with the atrial IEGM signals detected by said atrial detector, said control unit being configured to set the sensitivity of the atrial detector to a current one of said sensitivity settings corresponding to an expected P-wave amplitude in order to give the atrial detector a sensitivity that causes said atrial detector to detect a P-wave, if present in said IEGM signals, that has an amplitude above said expected P-wave amplitude; 
 a ventricular detector that detects ventricular contractions; 
 said control unit being connected to said ventricular detector and being configured to generate a signal indicating an occurrence of a premature ventricular contraction (PVC) when a ventricular contraction is detected by said ventricular detector that was not immediately preceded by detection of a P-wave in the IEGM signals detected by said atrial detector; 
 a memory; 
 a sensing unit, separate from said atrial detector and from said ventricular detector, also configured to receive said incoming atrial IEGM signals, said sensing unit being configured to, within a limited time duration, enter actual signal portions of said IEGM signals that occur in said limited time duration into said memory independently of whether said signal portions are detected by said atrial detector, said signal portions of said IEGM signals in said memory each having a predetermined signal portion length; 
 an analyzing unit, having access to the memory, configured to execute an analysis routine to identify whether a signal portion detected by said sensing unit and stored in said memory contains a P-wave having a lower amplitude than said current sensitivity setting; 
 a threshold determining unit connected to said analyzing unit, said threshold determining unit, if said analyzing unit identifies P-waves, detected by said sensing unit and stored in said memory, having a lower amplitude than said current sensitivity setting, setting a threshold for a new sensitivity setting for said atrial detector based on said P-waves detected by said sensing unit and stored in said memory and identified in said signal portion by said analyzing unit; and 
 said control unit being connected to said threshold determining unit and changing said current sensitivity setting to said new sensitivity setting, having said threshold determined by said threshold determining unit, to cause said atrial detector to detect all atrial events so as to configure said control unit to avoid false PVC indications due to a P-wave being present in said IEGM signals but undetected by said atrial detector. 
 
     
     
       2. An implantable cardiac stimulation device as claimed in  claim 1  wherein said control unit, upon detection of a predetermined cardiac event in said atrial signals that pass through said atrial detector, causes said analyzing unit to execute said analysis routing for a sequence of said IEGM signals in said memory that immediately precedes said predetermined cardiac event. 
     
     
       3. An implantable cardiac stimulation device as claimed in  claim 1  wherein said control unit automatically determines a highest allowable sensitivity setting for said atrial detector by analyzing an actual noise level of said atrial detector. 
     
     
       4. An implantable cardiac stimulation device as claimed in  claim 1  wherein said control unit sets said atrial detector to an initial sensitivity setting determined by a measured amplitude of a P-wave detected by said atrial detector, multiplied by a factor in a range between 0.4 and 0.9.